Between the first episode of the Animé, and the first games, Red and Blue, when did Pikachu become fat?
On Yellow, when I played, you see Pikachu's backsprite being quite chubby. In the Animé, it's a normal size. Also, in the later generations, Pikachu is the average, medium size.
It's just kind of a trivial fact. Why did the creators do this?